Chapter_21多恩布什第十版.ppt

21 1 21 2 21 AdvancedTopics ItemItemItemEtc 21 3 Introduction Thischapteroffersadvancedmaterialpresentingtherevolutioninmacroeconomicsthathasdevelopedoverthelast30yearsWelookatfourtheoriesinthischapter RationalexpectationsTherandomwalkofGDPRealbusinesscycletheoryNewKeynesianmodelsofpricestickiness Thesemodelsyieldcontrastingconclusionsabouttheconductofmonetarypolicy buttheyarealikeintheiremphasisontheimportanceofconsistencybetweenmacroeconomicandmicroeconomictheory 21 4 RationalExpectationsEquilibriumModels Inarationalexpectationsequilibriummodel marketsclearandthereisnothingsystematicthatmonetarypolicycandotoaffectoutputorunemploymentTheterm rationalexpectationsequilibrium identifiestwokeyfeaturesofthisapproachItplacesweightontheroleofexpectations rationalones Economicagentsdonotknowthefuturewithcertainty basetheirplans decisionsontheirforecastsorexpectationsaboutthefutureIfagentsarerational theywilluseallavailableinformationwhenformingthoseexpectationsTherationalexpectationsmodelinsistsonequilibriumMarketsclearimmediately 21 5 RationalExpectationsEquilibriumModels ThefullneoclassicaltheoryofASassertsthat UnemploymentisalwaysatthenaturalrateOutputisalwaysatthefull employmentlevelAnyunemploymentispurelyfrictionalNeithermonetarynorfiscalpolicychangeswillhaveanysystematiceffectonoutputTherationalexpectationsequilibriumapproachoffersadeviationfromthatmodel Somepeopledonotknowtheaggregatepricelevelbutdoknowthenominalwageorpriceatwhichtheycanbuyorsell 21 6 RationalExpectationsEquilibriumModels AssumeasimpleADschedule 1 AssumeasimpleshortrunAScurve includingpriceexpectations 2 TheADandASequationscanbecombinedtosolveforoutput 3 andprices 4 intermsofmandothervariables RewriteADasp m v y equatingADandAS andsolvingfory 3 21 7 RationalExpectationsEquilibriumModels AssumeasimpleADschedule 1 AssumeasimpleshortrunAScurve includingpriceexpectations 2 TheADandASequationscanbecombinedtosolveforoutput 3 andprices 4 intermsofmandothervariables Pluggingequation 3 intotherewrittenADschedule andsolveforpyields 4 21 8 RationalExpectationsEquilibriumModels Together equations 3 and 4 tellustheequilibriumoutputandpricesinourmodeleconomyIfmoneysupplyrises1percent outputrisesby1 1 percentandpricesriseby 1 percentIfm v andy areknown givenpriceexpectations predictionsforyandpcanbecalculatedusingequations 3 and 4 Oftenthemodelgeneratesvaluesthataredifferentfromexpectations thestandardAS ADmodelassumesthateconomicagentsmakepredictionsfortheeconomythatareinconsistentwiththepredictionsthemodelitselfmakes TheLucasCritique 21 9 ThePerfect ForesightModel Thepreviousmodelcanbealteredtoassumethateconomicagentsarecorrectintheirpredictions orp peEconomicdecisionmakersuseequation 4 topredictpricesandcomputepe 5 Collectingtermscontainingpe wecanrearrange 5 togivetheperfectforesightforecastandsolutionforthepricelevelandthecorrespondingsolutionforoutput 6 7 21 10 ThePerfect ForesightModel Theperfect foresightpredictionsinequations 6 and 7 arequitedifferentfromtheoriginalAS ADpredictionsembodiedinequations 3 and 4 ThelatterassumeexogenouslygivenpriceexpectationsTheformerassumethatpriceexpectationsareformedendogenously andthatexpectationformationisconsistentwiththepredictionsofthemodelThesedifferenceshaveimplicationsfortheeffectivenessofmonetarypolicyUnderaperfectforesightmodel A1 increaseinthemoneysupplyleadstoexactlya1 increaseinthepricelevelA1 increaseinthemoneysupplyleadstoNOincreaseinoutput 21 11 ARationalExpectationsModel Arationalexpectationsmodelassumesthat AgentsmakethebestuseofwhateverinformationisavailabletothemExpectationsareformedinamannerconsistentwiththewaytheeconomyactuallyoperatesSimilartoaperfectforesightmodelinwhichsomeofthekeyvariablesareuncertainSupposebeforemoneysupplyisknown economicdecisionmakersexpectthemoneysupplytoequalmeIfthemoneysupplyturnsouttobem thedifferencebetweenagents expectationsandtheactualmoneysupplyis 21 12 ARationalExpectationsModel Themonetarypolicymultiplierwithrespecttoanticipatedmoney me iszero justasintheperfect foresightmodelThemonetarypolicymultiplierwithrespecttounanticipatedmoney m ispositive justasintheAS ADmodelTheequilibriumsolutionsforpriceandoutputare 11 12 21 13 ARationalExpectationsModel Theeffectofanincreaseinthemoneysupplyunderrationalexpectationsmustbebrokendownintotwoparts TheeffectofananticipatedincreaseinthemoneysupplyRationalexpectationspredictsNOeffectonoutputRationalexpectationspredictsanequalchangeinpricesTheeffectofanunanticipatedincreaseinthemoneysupplyRationalexpectationspredictsanincreaseinoutputof1 1 Rationalexpectationspredictsanincreaseinpricesof 1 21 14 TheRandomWalkofGDP FluctuationsinoutputcanbetransitoryorpermanentIffluctuationsareprimarilypermanent changesinADmustbeofrelativelylittleimportance AccordingtotheAS ADmodel theeffectofADshockswearsoffwithtimebecausethelong runaggregatesupplycurveisverticalIftheeffectofshocksispermanent theirsourcemustbesomethingotherthanaggregatedemandTheideathatchangesinoutputarepermanentcanbedescribedbysayingthatGDPfollowsarandomwalkHavingwanderedupordown GDPhasnotendencytoreturntotrend starkcontrasttoimplicitmodeloftext 21 15 TheRandomWalkofGDP NelsonandPlosserchallengedthepredominatingideathat GDPfluctuatesaboutasmoothtrendlineShockstoADaretheprimarycauseofthetransitoryfluctuationsSuggestedthatthetrendisnotsosmoothandissubjecttolargeandfrequentshocksthathaveapermanenteffectonthelevelofGDPFigure21 3presentsastylizedviewoftrendgrowthandfluctuationsaroundthetrend InsertFigure21 3here 21 16 TheRandomWalkofGDP Needtodetrendthedata Supposethetrendinycanberepresentedbyaliteraltimetrend 22 Equation 22 statesthatyrisesby ineverytimeperiodSubtractinglastperiod syfromeachsideoftheequationyields 23 OR 24 Equations 22 and 24 areequivalenttooneanother 21 17 TheRandomWalkofGDP Supposeweaddanoutputshock ut toequation 22 25 Alternatively theshockcouldbeaddedtoequation 24 26 Accordingtoequation 25 theeffectofashocklastsoneperiodCanbemadestationarybytakingoutatimetrend trendstationaryDominatedbytransitoryshocksAccordingtoequation 26 theeffectofashockonthelevelofyispermanentCanbemadestationarybydifferencing differencestationaryDominatedbypermanentshocks 21 18 TheRandomWalkofGDP AccordingtotheAS ADmodel BusinesscyclescausedbyADfluctuationsarerelativelyshort livedShockstoASmightbepermanentifthederivedfrompermanentproductivityimprovementsNelsonandPlossershowedthatGDPincludesbothpermanentandtransitoryshocks butGDPprocessdominatedbypermanentshocksFigure21 4showstheimportanceofpermanentshocksPrior1973consistentwithfluctuationsabouttrendPost1973apermanentdownwardshift InsertFigure21 4here 21 19 TheRandomWalkofGDP Theideathatshockswithlong lastingimpactareimportanttotheeconomyisnowgenerallyacceptedTheinferencethatADisrelativelyunimportantremainscontroversialAnalternativeviewisthatlargeandrelativelypermanentaggregatesupplyshocksoccur butonlyonrareoccasionsInbetween ADshocksdominate PierrePerron Trendstationarywithbreaks Importanceofaggregatedemandshocksremainsacontroversialarea 21 20 RealBusinessCycleTheory RBCtheoryassertsthat FluctuationsinoutputandemploymentaretheresultofavarietyofrealshocksthathittheeconomyMarketsadjustrapidlyandremaininequilibriumRBCtheoryisthenaturaloutgrowthofthetheoreticalimplicationof Therationalexpectationsapproach anticipatedmonetarypolicyhasnorealeffectTheempiricalimplicationoftherandomwalktheory aggregatedemandshocksarenotanimportantsourceoffluctuations 21 21 RealBusinessCycleTheory RBCmustdotwothings ExplaintheshocksthathittheeconomyExplainthepropagationmechanisms mechanismthroughwhichadisturbanceisspreadthroughtheeconomyWhydoshockstotheeconomyseemtohavelong livedeffects TheintertemporalsubstitutionofleisureisthepropagationmechanismthatismostassociatedwithequilibriumbusinesscyclesWhydopeopleworkmoreatsometimesthanatothers DuringboomsemploymentishighandjobsareeasytofindDuringrecessionsemploymentislowerandjobsarehardtofind Empiricalevidencedoesnotsupporttheexplanationthatpeopleworkmorewhenwagesarehigher 21 22 RealBusinessCycleTheory RBCmodelsexplainlargemovementsinoutputwithsmallmovementsinwagesasfollows ThereisahighelasticityoflaborsupplyinresponsetotemporarychangesinthewagePeoplearewillingtosubstituteleisureintertemporallyPeoplecareabouttheirtotalworkeffectbutcareverylittleaboutwhentheyworkSupposethatwithinatwo yearperiodtheyplantowork4 000hoursatthegoingwageIfwagesareequalinthetwoyears theywouldwork2 000eachyearIfwagesare2 higherinoneyearthantheother theymightwork2 200inthehighwageyear and1 800intheother 21 23 RealBusinessCycleTheory RBCmodelsexplainlargemovementsinoutputwithsmallmovementsinwagesasfollows ThereisahighelasticityoflaborsupplyinresponsetotemporarychangesinthewageLaborisnotsensitivetopermanentchangesinwagesIfthewagerises andwillremainhigh thereisnothinggainedbyworkingmoreinoneyearoveranotherTheintertemporalsubstitutionofleisureisclearlycapableofgeneratinglargemovementsintheamountofworkdoneinresponsetosmallshiftsinwagesCouldaccountforlargeoutputeffectsinthecycleaccompaniedbysmallchangesinwages 21 24 RealBusinessCycleTheory Themechanismsthatpropagatebusinesscyclesaresetinmotionbyevents disturbancesthatchangetheequilibriumlevelsofoutputandemploymentinindividualmarketsandtheeconomyasawholeThemostimportantdisturbancesinRBCtheoryare ShockstoproductivityorsupplyshocksWeather newmethodsofproductionShockstogovernmentspending Theevidencefortheimportanceofmoneyseemspersuasive makingitdifficultforproponentsoftheRBCtobesuccessfulatconvertingtheprofessiontotheirviews 21 25 NewKeynesianModelsofPriceStick